Colorimetric testing is utilized in many industries to determine the presence or degree of presence, e.g. concentration in solution, of particular substances. For example, chlorine test kits have been used to determine the general concentration of chlorine level in swimming pools. In another example, early pregnancy tests detect the presence of a certain hormone in female during pregnancy. Both of these examples illustrate the use of a colorimetric test to determine the presence or degree of presence of a substance. In these examples, the color change is visible to the human eye and is typically observed directly by a person conducting the test.
United States Patent Application Publication US20090325300 describes a card component for use in conjunction with a spectral detection unit useful for detecting trace materials including biohazards, toxins, radioactive materials, narcotics, and explosives. In particular, US20090325300 discloses, at paragraph [0043], that a sample of an unknown trace material is collected on a card component. Reaction of the unknown trace materials sample collected on the on the pad is initiated with liquid reagents and dissolved compounds contained in at least one flexible walled capsule embedded in the card component, wherein the reaction is initiated after inserting the card in the chemical detection unit causing walls of the capsules to yield to fluid flow, establishing fluid communication between the capsules and the pad. This is accomplished by releasing chemicals and other contents of the first capsule and applying heat to stimulate reaction with the unknown trace material. The fluid communication may be established via specific paths like grooves or similar structural means, or using wicks. Further, chemicals from the capsules may be released in a fashion to react in spatially distinct regions of the pad or the regions may be temporally separated for chemical reactions. The spectral pattern is observed and recorded by the chemical detection unit. With respect to release of chemicals from capsules to react in spatially distinct regions of the reaction pad, US20090325300, at paragraph [0047] discloses that that in an embodiment the reaction pad can be divided into three separate fluid channels each in proximity to a specific capsule. In this way three separate color reactions can be produced spatially in a side-by-side configuration rather than in timed sequence. With respect to release of chemicals from capsules to temporally separated regions of the reaction pad, US20090325300, at paragraph [0049], discloses that in one preferred embodiment the first of two capsules capsule is activated and any sequence of color changes is recorded. The second capsule is then activated and the color recorded.
In some colorimetric tests a prior chemical reaction modifies the characteristics of the substance under test in order to be able to execute a subsequent test that requires molecular modification prior to testing for a particular substance. A well-known example is the application of the Griess reaction as the second stage of a two stage reaction scheme to detection of nitroglycerin. The reaction scheme involves two solutions. In the first stage, the reaction scheme involves adding a preliminary alkaline solution containing a base to nitroglycerin to produce nitrite ions. In the second stage, the reaction scheme involves adding an acidic solution Griess reagent mixture to the nitrite ions to produce a colored product. An exemplary base is sodium hydroxide. An exemplary acid Griess reagent mixture includes sulphanilamide and 2-naphthylamine in a phosphoric acid solution. The Griess reaction involves reaction of sulphanilic acid with the nitrites to produce diazonium ions, coupled with reaction of the dizonium ions react with 2-naphthylamine to produce a colored Griess reaction product, both occurring in the same Griess solution. It is desirable to time adding the preliminary alkaline solution containing a base prior to adding the acidic Griess solution containing the Griess reagent mixture because the reaction conditions of the first stage are alkaline and the reaction conditions of the Griess reaction are acidic, therefore differing in pH. Combining the alkaline and acidic solutions would tend to neutralize the pH, thus negatively affecting the test.
Notwithstanding the above teachings, there remains a need for colorimetric test systems and methods that provide for accurate timing control and sequencing of different chemicals. More particularly, there remains a need for colorimetric systems and methods for controlling the arrival of chemicals to a reaction pad in a colorimetric card that do not require temporally separate release of the chemicals.